At least a print head and an ink tank are used for ink jet printing. The print heat ejects ink and the ink tank accommodates ink to be supplied to the print head. The ink is consumable. Accordingly, an ink jet printing apparatus is configured so that the ink tank can be detachably installed in the ink jet printing apparatus, independently or in a cartridge form integrated with the print head, to replace the ink tank with a new one when the ink in the ink tank is exhausted.
For conventional ink jet printing apparatuses, techniques have been proposed and put to practical use, the techniques which detect the presence or absence of ink in the ink tank in order to show a user when to replace the ink tank. The methods described below are used to sense the presence or absence of the ink.
(1) In one method, it is detected that the ink has reached a predetermined level (the level of the ink), using that a pair of electrodes is provided in the ink tank and a current flows between the electrodes via the ink.
(2) In another method, it is detected that the ink has reached the predetermined level, using that a prism having a refractive index similar to that of the ink is provided on an inner wall surface of the ink tank and the refraction of light varies depending on whether the level of the ink is higher or lower than the position of the prism when light is incident on the prism
(3) In furthermore another method, it is detected that the ink has reached the predetermined level, using a variation in the capacitance between the ink in the ink tank and an electrode provided outside the ink tank. These methods may be combined with one another or with a method called dot count which converts the number of ink ejections or the like into the amount of ink used.
With reference to FIGS. 10A to 10C, description will be given of an example of a conventional detecting system that optically detects the ink remaining amount and that is included in the above described methods.
FIG. 10A shows a sectional view of a conventional ink tank 101 comprising means for optically detecting the ink remaining amount. Further, FIG. 10B shows a perspective view of a cup portion 102 of the ink tank 101.
The ink tank 101 has a cup portion 102 and a cover portion 103. Ink is housed in a housing 104 composed of the cup portion 102 and the cover portion 103. The interior of the housing 104 is divided into two spaces by a partitioning wall 114 having a communication channel 109 at the lower end and being formed in the cup portion 102. One of the spaces is an ink accommodating chamber 106 closed except for the communication channel 109 to directly accommodate ink. The other space is a negative pressure generating member housing chamber 105 that houses a negative pressure generating member 111 that absorbs and holds the ink. An ink supply port 110 and an air-through hole 108 are formed in a wall forming the negative pressure generating member housing chamber 105. The ink supply port 110 is used to supply the ink to a print head portion (not shown) and the air-through hole 108 is used to introduce external air into the ink tank 101 as the ink is consumed. In FIG. 10A, the shaded portion shows an area in which a negative pressure generating member 111 holds the ink.
A gas introduction groove 119 extending upward from the communication channel 109 is formed in a wall surface of the partitioning wall 114 which faces the negative pressure generating member housing chamber 105. The gas introduction groove 119 facilitates the introduction of the air from the negative pressure generating member housing chamber 105 into the ink accommodating chamber 106. Further, inside the negative pressure generating member housing chamber 105, the negative pressure generating member 111 is not present in a space (buffer portion) around the air-through hole 108.
The ink in the negative pressure generating member 111 is consumed by the print head portion and thereby a gas-liquid interface 111a in the negative pressure generating member housing chamber 105 is decreased down to the upper end of the gas introduction groove 119 shown in FIG. 10A. The subsequent ink consumption causes air to be introduced into the negative pressure generating member housing chamber 105 through the air-through hole 108. The introduced air enters the ink accommodating chamber 106 through the communication channel 109. Instead, the ink in the ink accommodating chamber 106 enters the negative pressure generating member housing chamber 105 through the communication channel 109. The ink is then filled into the negative pressure generating member 111. This operation is called a gas-liquid exchanging operation.
Accordingly, even when the ink in the negative pressure generating member housing chamber 105 is consumed by the print head portion, the negative pressure generating member 111 is filled with an amount of ink from the ink accommodating chamber 106 which corresponds to the consumed ink. The gas-liquid interface 111a in the negative pressure generating member housing chamber 105 is thus maintained at an almost fixed height. That is, the negative pressure generating member 111 holds an almost fixed amount of ink to maintain an almost fixed negative pressure on the print head portion. Consequently, the print head portion is stably supplied with ink.
A triangular-prism-shaped optical reflector 113 is placed on a bottom surface of the ink accommodating chamber 106. The optical reflector 113 is integrated with the cup portion 102 and its vertex has an angle of 90°. On the other hand, in the ink jet printing apparatus in which the ink tank 101 is installed, an optical sensor module 151 is placed below the optical reflector 113 as shown in FIG. 10C. The optical sensor module 151 has a light emitting portion 152 and a light receiving portion 153.
If there is no ink in the ink accommodating chamber 106, light emitted by the light emitting portion 152 enters the optical reflector 113 and is reflected by two slopes of the optical reflector 113 to return to the light receiving portion 153 as shown by the solid arrow in FIG. 10C. If ink is present at a position higher than that at which the light enters the slope of the optical reflector 113, light emitted by the light emitting portion 152 enters the optical reflector 113 and most of the light is then transmitted through the optical reflector 113 as shown by a dashed arrow. Consequently, the presence or absence of ink can be detected on the basis of the intensity of light returning to the light receiving portion 153.
Patent Document 1 (Patent Document 2) also discloses the configuration of an ink tank having an optical ink remaining amount detecting means as described above.
In recent years, many full-color ink jet printing apparatus have been developed which tend to use an increasingly large number of ink colors. Thus, more and more types of ink tanks have been mounted in the ink jet printing apparatuses. Some ink tanks are provided with inherent information in order to prevent erroneous installation. Known methods for proving the ink tank with inherent information include providing the ink tank with a mechanical ID (identifier) structure, bonding a bar code label to the ink tank, or providing the ink tank with an information storage element such as a ROM.
As described above, the conventional ink jet printing apparatuses use an increasingly large number of colors in order to meet the need for high-grade printing. Correspondingly, more and more types of ink tanks are mounted in the conventional ink jet printing apparatuses. On the other hand, there has been a growing demand for downsizing in order to minimize installation area or to improve portability for mobile use. Downsizing the ink jet printing apparatus requires downsizing the ink tank and simplifying the structure of the ink remaining amount detecting means.
Further, information on the detected ink remaining amount is conventionally transmitted to the ink jet printing apparatus, which then warns the user to exchange the ink tank. As previously described, some ink tanks have inherent information. However, such information relates to, for example, the type of ink accommodated and is required to prevent erroneous installation.
However, there have been no techniques which can detect information on ink using a simple structure and which can simply and reliably store the detected information in the ink tank.
Patent Document 1: Japanese Patent Application Laid-open No. 7-164626
Patent Document 2: U.S. Pat. No. 6,137,503